1. Field
The present invention relates generally to communications, and more specifically to a novel and improved method and apparatus for dynamic channelization code allocation in a communication system.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard), (4) a data-only communication system such as the high data rate (HDR) system that conforms to the TIA/EIA/IS-856 standard (the IS-856 standard), (5) a system combining features of a system like the IS-2000 standard with features similar to the IS-856 standard, such as detailed in documents entitled “Updated Joint Physical Layer Proposal for 1xEV-DV”, submitted to 3GPP2 as document number C50-20010611-009, Jun. 11, 2001; “Results of L3NQS Simulation Study”, submitted to 3GPP2 as document number C50-20010820-011, Aug. 20, 2001; “System Simulation Results for the L3NQS Framework Proposal for cdma2000 1xEV-DV”, submitted to 3GPP2 as document number C50-20010820-012, Aug. 20, 2001, and related documents generated subsequently (the 1xEV-DV proposal), and (6) other standards.
Communication with multiple mobile stations may be supported using various types of channels in a wireless communication system, such as those listed above. For example, voice communications may be supported using a dedicated channel for each active voice call. Dedicated data channels may also be supported. In this situation, the number of simultaneous users served by a base station within given spectrum is limited by the supportable number of dedicated channels. One or more shared channels may also be deployed. Multiple mobile stations may access a shared channel using one of a variety of multiple access techniques, known in the art. Additional channels may be reserved for various signaling and system support functions. Each of the various systems listed above may provide support for multiple dedicated channels, one or more shared channels, or a combination of both.
In a CDMA system, various channels can be distinguished through the use of channelization codes. Example channelization codes are orthogonal codes such as Walsh codes or Orthogonal Variable Spreading Factor (OVSF) codes. There are a limited number of codes available for a given spreading factor (SF), and thus the number of channels, including dedicated and shared channels, is limited for a given code space. In IS-95 systems, the forward link capacity is limited by interference, and therefore the code space is sufficient for the number of supportable channels. However, advances in more recent systems reduce the effects of interference, allowing for additional simultaneous users, and thus increasing demand for codes to support the additional channels.
Furthermore, channels using higher data rates may be desired. A higher data rate may be transmitted with a smaller spreading factor. Increased use of smaller spreading factors reduces the overall number of codes available.
Increase demand for codes, reduced available codes, or a combination of the two factors may cause the code space to be depleted in a given system configuration. Thus, capacity will be limited in situations where, due to advances in interference mitigation, additional users and/or increased data throughput would otherwise have been available. There is therefore a need in the art for efficient allocation of channelization codes.